Abstract: A case study on a 66 m long connecting gallery between Ziyang station and Wuliting station of Fuzhou metro line 2 is conducted to summarize the design and construction techniques of the freezing method of the ultra-long connecting gallery (over 60 m) in a complex environment. Optimization measures, such as double collecting well structures and connecting gallery dimension reduction, are implemented during the design phase. The following pivotal techniques are proposed: (1) Drilling azimuth angle is measured by a high-precision inclinometer, and the drilling parameters are appropriately set. (2) Freezing curtain size and freezing period are appropriately set and optimized. (3) Secondary support and zone excavation methods are used. (4) Grouting holes are appropriately set, and the fine tracking grouting is used to control the surface settlement. The analysis of the measured data of freezing measurement and surface settlement show that the techniques used can guarantee the freezing quality, control the frost heaving and thawing settlement, and minimize the influence on the surroundings, resulting in the successful completion of the super-long connecting gallery.

Key words: ultra-long connecting gallery, structural optimization, artificial freezing, drilling and deviation correction; settlement